1. Technical Field
This disclosure relates to a cleaning blade, and to an image forming apparatus and a process cartridge, which use the cleaning blade.
2. Description of the Related Art
In electrophotographic image forming apparatuses, residual toner remaining on the surface of an image bearer such as photoconductors even after a toner image thereon is transferred onto a recording medium or an intermediate transfer medium is removed therefrom using a cleaner.
A cleaning blade is typically used as a cleaning member of such a cleaner because of having advantages such that the cleaner has simple structure and good cleanability. Such a cleaning blade typically includes an elastic member made of a gum elastic such as polyurethane rubbers, and a supporting member to support the elastic member. The cleaning blade typically has a configuration such that one end of the elastic member is supported by the supporting member, and an edge (i.e., tip edge) of the other end (i.e., free end) of the elastic member is contacted with a surface of an image bearer to block and scrape off residual toner on the surface of the image bearer, thereby removing the residual toner from the surface of the image bearer.
In attempting to fulfill a recent need for high quality images, there are image forming apparatuses using toner (hereinafter sometimes referred to as polymerization toner), which is substantially spherical and has a relatively small particle diameter and which is prepared by a method such as polymerization methods. Since polymerization toner has such an advantage as to have a higher transfer efficiency than pulverization toner, which has been conventionally used for image forming apparatuses, the polymerization toner can fulfill the need. However, polymerization toner has such a drawback as not to be easily removed from an image bearer by such a cleaning blade as mentioned above, resulting in occurrence of defective cleaning (hereinafter referred to as a toner passing problem). This is because such polymerization toner has a high circularity and a small particle diameter, and therefore easily passes through a small gap between the tip of a cleaning blade and the surface of an image bearer.
In attempting to prevent occurrence of such a toner passing problem, a technique such that the pressure to a cleaning blade contacted with the surface of an image bearer is increased (i.e., contact pressure of a cleaning blade is increased) is often used to enhance the cleanability of the cleaning blade. However, it is well known that when the contact pressure of such a cleaning blade is increased, the following problem is caused.
Specifically, as illustrated in FIG. 2A, when the contact pressure of a cleaning blade 62 is increased, the friction between the cleaning blade 62 and a member 123 to be cleaned (hereinafter sometimes referred to as an image bearer) is increased, and a tip edge 62c of a tip surface 62a of the cleaning blade 62 is pulled by the moving surface of the image bearer 123 in the moving direction of the image bearer, thereby everting the tip edge portion of the tip surface 62a of the cleaning blade 62. In this regard, since the thus everted tip edge portion of the cleaning blade 62 is returned to the original state due to the restoring force of the cleaning blade. In this case, an abnormal sound is generated. Since the eversion and restoration of the tip edge portion are repeated, the tip edge portion tends to vibrate, resulting in generation of fluttering sounds (i.e., occurrence of a fluttering sound problem).
When the cleaning operation is continued while the tip edge portion of the cleaning blade 62 is everted, the a portion X of the tip surface 62a of the cleaning blade 62, which portion is few micrometers away from the tip edge 62c, is abraded as illustrated in FIG. 2B. When the cleaning blade 62 is further used for the cleaning operation, the tip edge portion of the tip surface 62a of the cleaning blade 62 is further abraded, resulting in lack of the tip edge 62c of the cleaning blade 62 as illustrated in FIG. 2C. The cleaning blade 62 having no tip edge hardly removes residual toner from the surface of the image bearer 123, thereby causing a cleaning problem in that an abnormal image such that background of an image is soiled with residual toner is formed. Therefore, a need exists for a cleaning blade which can maintain good cleanability without being everted even when the contact pressure of the cleaning blade is increased.
FIGS. 2A-2C will be described later in detail.
In addition, in attempting to solve the problem in that the portion (i.e., tip edge portion, hereinafter sometimes referred to as a abutment part) of a cleaning blade contacted with an image bearer is everted, it is attempted to increase the hardness of the abutment part so that the abutment part is hardly deformed.
For example, a cleaning blade made of a polyurethane elastomer is proposed in which the abutment part thereof is coated with a resin having a pencil hardness of from B to 6H to enhance the angular accuracy of the edge while decreasing the friction coefficient of the cleaning blade.
In addition, a cleaning blade is proposed which includes a urethane rubber blade and a silicon-including layer formed on the abutment part of the rubber blade, wherein the surface of the silicon-including layer is cured. It is described therein that a good combination of low frictional property and abrasion resistance can be imparted to the blade.
Further, a cleaning blade is proposed which includes an elastic blade and an outermost layer formed on the tip edge portion of the elastic blade, wherein the tip edge portion has been subjected to a low friction coefficient treatment, and wherein the outermost layer is harder than the elastic blade. It is described therein that the blade can maintain good cleanability with hardly causing the flattering sound problem.